Voucher contingency management (CM) interventions are efficacious in enhancing retention in treatment and reducing drug use, but they have not been implemented widely in community-based programs. A lower-cost CM procedure, that provides opportunities to win prizes ranging in value from $1 to $100, shows efficacy in retaining substance abusers in an HIV drop-in center (Petry et al., 2001 a), as well as in reducing substance use in traditional, community-based treatment programs (Petry et al., 2000; Petry & Martin, in press). The purpose of this study is to evaluate the efficacy of this CM technique in enhancing attendance, reducing drug use, and improving health among clients attending HIV drop-in centers. Specifically, 172 clients will be randomly assigned to one of two 6-month treatment conditions: standard 12-step oriented group treatment, or CM group treatment. In the CM group, clients earn the chance to win prizes for submitting clean urine specimens and for complying with steps toward their treatment goals. Activities related to improving health will be emphasized, such as attending medical appointments, recording daily medication consumption, getting prescriptions filled, and attending medication adherence support groups. Group attendance, drug use, medical problems and services received, and risky drug use and sexual behaviors will be measured pre-treatment, at months 1, 3 and 6, and at 9- and 12-month follow-up evaluations. Compared to the control condition, we expect that those assigned to the CM condition will show greater retention in treatment, reductions in drug use, improvements in health, and decreases in risk behaviors. This study represents an important extension of our previous and ongoing work in low-cost CM in that it involves a specific population of substance abusers (HIV-positive), expands our work to non-traditional, community-based settings (drop-in centers), and implements the CM approach in a group (rather than individual) format.